Antenna coupling circuits



Nov. 18, 1941. w. H. NEWBOLD 2,262,956

ANTENNA COUPLING CIRCUITS Filed Mziy'l, 1940 Patented Nov. 1 8, 1941 ANTENNA COUPLING outcorrs William H. Newbold, LanghorneQPa assignor to I Philco Radio and Television Corporation,

Philadelphia, Pa., a corporation of Delaware Application May 1, 1940, Serial No. 332,827

16 Claims.

This invention relates to antenna coupling circuits, and more particularly to means for coupling a conventional antennato a radio receiver of the type whose input circuit comprises a tuned loop circuit.

Because of the unusual convenience and advantages afforded by receivers employing resonant loops, it has been found desirable in many instances to provide radio receivers with input circuits which consist of a tuned resonant loop circuit. However under certain conditions the loop may fail to provide an adequate signal, and for this reason it is desirable to adapt such receivers for optional operation from a more conventional antenna such as, for example, an elevated wire system. This is of particularv importance where it may be necessary to operate the receiver in a shielded location.

In general it has been found desirable, when employing a conventional outside antenna with such receivers, to utilize the loop circuit as the receivers tuned input circuit, and to couple the conventional antenna to the loop, rather than to provide a complete auxiliary tuned circuit for use only with the outside antenna. The latter practice would result not only in the duplication of elements, but would likewise complicate the switching required in changing from loop operation to conventional antenna operation.

Heretofore it has not been uncommon to couple the antenna into the loop by connecting the antenna to an intermediate tap on the loop windins. preferably through a small condenser, as shown in the copending application of David Grimes, Serial No. 277,276, filed June 3, 1939. Similarly it is known to couple the antenna tothe loop inductively by means of a oneor two-turn winding wound over and parallel to the loop winding. It has been found, however, that receivers so coupled to conventional antennas yield a performance which is markedly inferior 'to that of receivers specifically designed to operate from such an antenna.

With the foregoing in mind, it is an important object of this invention to provide an antenna coupling circuit for a loop-equipped radio receiver which will enable the receiver to operate at high efiiciency on either its loop or on a con-' ventional antenna.

A further object of the invention is to provide a means for coupling a conventional antenna into a resonant loop through a high impedance primary winding.

, Still another object of the invention is to combine the advantages of a high impedance antenna primary with a set designed for loop operation.

These and other objects, and the realization thereofby the present invention, will be fully understood by reference to the accompanying drawing, in which a Fig. l is a schematic diagram illustrating one method of coupling an antenna into a resonant loop circuit by means of a high impedance primary and a relatively low impedance secondary; and

Fig. 2' is a schematic-diagram showing a modifled form of theinvention.

In each of the figures there is shown a tuned loop circuit comprising a loop winding I which may consist of one or more turns of a suitable conductor, and a variable tuning condenser 2 for tuning the loop to resonance with a desired'radio frequency signal. The signal voltage output of the loop circuit may be connected tothe input circuit of a vacuum tube V1 from whence it may be supplied to any suitable signal utilization means. The antenna denoted by the reference numeral 3 may be any one of a wide variety of conventional systems, such as the usual elevated wire or flat top antenna.

Attention isnow directed to Fig. 1 in which the antenna 3 is coupled into the resonant loop circuit (p winding I and tuning condenser) by means of a transformer comprising a primary winding 4, and a secondarywinding 5 serially connected in the resonant loop circuit. If desired, .the transformer may be provided with a comminuted iron core 6. The primary winding l may advantageously be of high impedance and may be designed to resonate near the low frequency end of the desired frequency band when tne antenna 3 is connected to the winding. Preferably the self-resonant frequency of the winding t, with antenna attached, will lie outside of and below the band of frequencies which it is desired toreceive.

In general the inductance of the secondary winding 5 should not be large compared to the inductance of the loop winding l, and preferably theinductance of winding 5 is less than that of winding I. The degree of coupling between the windings 4 and 5 will depend upon the relative values of inductances I and 5, but in general as the ratio of inductance 5 to inductance l de-- creases, the coupling between windings 4 and 5 should be increased. In this way, the optimum coupling between the antenna circuit 3, 4 and the resonant loop circuit l 5, 2 may be maintained regardless of the ings l and 5. r

In practice,'in order to decrease the gain of the circuit at frequencies below the desired frequency band, e. g. at the intermediate frequency of a superheterodyne receiver, it has been found desirable in some cases to provide a short circuited Winding 1 on the coupling transformer. The winding 1, which may be of one turn, will have negligible effect on the signal transfer over thedesired frequency band. Similarly in order to increase the gain at the high frequency end ,of the band, it may be desirable to windthe coils 4 and 5 in such a manner that the capacity coupling therebetween aids the inductive cou pling. Such windings are well known the art;

and hence require no descriptionQ 7 a V 7 The winding 5 is preferably characterized by a high ratio of reactance to resistance,. -i. e a high Q, where H I wL I Q thcv enerally accepted figure of merit forcoils.

If the Q of coil 5 be made, greater than the Q of the loop winding I, the selectivityof the loop circuit may be increased over; that obtaining without thewinding- 5. And if the Q o coil 5 be made greater than'twice that of the loop I, the

sensitivityofzthe loop circuit may be made greater than it Would be without the coil 5. The properties of loop .circuits having serially inserted high-Q inductors are fully described andclaimed in a copending application; of William H.

Grimditch, Serial No. 279,745, filed June 1'7, 1939. 7;

In Fig. 1, the circuit is shown adapted for use with the antenna3. If conventional loop reception is. desired, this may besecured merely -by disconnecting the antenna 3. ,With antenna 3 disconnected, it is possible that, the 'vvinding l may be self-resonant ,atgsome point within the desired bandof frequencies and thnsact as a 'l adcn, t 9p ircu i, 5.1.1, h s may be tween the high potential end of the loop and the grid of tube Vi it'will 'belobvious'that the wind ing might'fjust' as: readily becohnect'ed between the low potentiafend of the-loopand ground; by inserting it at the pointm'arked 'X. In one embodiment of the latter connection, thefollow ingya'lues of inductanc'ef'g'ave very satisfactory results: primary winding' lj 1750. microhenrysj' secondary winding 5, 16 microhenr'ys'; loopwind-i mg I, "150 microhenrysf mutual i'nductancebetween windings 4 and" 5, 130' microhenrys;

- Reference is'now made to-Figl 2 in which there isillustrated a-modification of the invention; In this embodiment/the"antenna 3- is inductively coupled directlyto-the -loop winding" 1 i by means of a suitable priin-ary winding 9 positioned adjacent toa portionof the'winding l. By-posi tioning the primary-winding 9-in a" corner of the loop winding as shown,'sumcient coupling be-- specific inductances of, the windof the .coil 9 are similar to those discussed hereinbefore with reference to the coil 4. Generally speaking the diameter of the coil 9 should be sufliciently great to permit the realization of the desired coupling between it and the loop winding I. In one physical embodiment of the invention, the coil 9 was about 3 inches in diameter and'had an inductance of approximately 2 millihenrys. The loop Winding l was wound on a frame measuring about 8 by 14 inches. A suit-- able means 8 may be provided for short-circuiting the coil 9 whenloop reception is desired. While the invention has been described with particular reference to the embodiments of the drawing, it'will be understood that the invention is capable of various forms of physical expression, and is,'therefore, not to be limited to the specific disclosure, but only by the scope of the appended claims.

I claim:

.1. Anantenna circuit-for a radio receiver, constructed and arranged to provide reception selectively fro-m a loop or from an external antenna,..comprising a loop winding and a tuning condenser connected to form a resonant loop tuning circuit capable of being tuned over a pre determined range of frequencies, an external antenna, a circuit including a high impedance primary winding inductively coupled to said tuning circuit, said primary winding being self-resonant nearpthe low frequency end of the tuning range of said tuning circuit, and a connection fromsaidsantenna to said high impedance primary tweenthe windings may read'ily be secured. The

winding.

2. An antenna circuit for a radio receiver according to claim 1, characterized in that some capacitivecoupling is additionally provided be-,

tween said primary winding and said tuning cir-- cuit, said primary winding being wound in a direction such that the capacitively transferred signal; aids the inductively transferred signal.

i 3. An antenna circuitfor a radio receiver, co n-" structed and arranged to provide reception selec: tively from a loop or from an external antenna, eomprising a loop winding and a tuning con denser connected to form a resonant loop tuning circuit eapableof being tuned overa predetere minedrange of frequencies, an external antenna, and a coil having a high inductance connected between said antenna and a point having a negligible radio frequency potential to ground,

said coil together with said antenna forming. a

circuit which is self resonant below the tuning range of 'said'tuning circuit, the circuit compris ing said antenna and said'coil' being inductively coupled to said tuning circuit. 4. nnantenna circuit for a radio receiver, constru'ct'edand arranged to provide reception selectively/from a loopor' from an external antenna,

comprising a loop winding, a coupling winding,

and a tuning condenser connected to form a resonant loop tuning circuit capable of being tunedover a" predetermined range offre'quencies, an external antenna and a high impedance pri-' mary Winding in *circuit itherewith; said lastinductively coupled to said named Winding "being coupling winding;

'5. An antenna circuit as claimed in claim 4;

characterizedin that the inductance of" saidcoupling Winding is small compared to the inductance ofsaid loop Winding.

6.Anantenna'circuit as claimed in claim 1,

comprising means. for J short circuitingsaid pri-- I mary winding at will, whereby loop receptionobtains over said predetermined range offrequencies substantially without effect by said primary winding.

'7. An antenna circuit as claimed in claim 4, wherein said coupling winding has a higher Q than said loop Winding.

8. An antenna circuit for a radio receiver, constructed and arranged to provide reception selectively from a loop or from an external antenna, comprising a loop winding and a tuning condenser connected to form a resonant loop tuning circuit capable of being tuned over a predetermined band of frequencies, an antenna system including an external antenna, and a high inductance primary coil connected in said system, said primary coil being self resonant near the low "frequency end of said band of frequencies, and being constructed and arranged to provide a predetermined coupling between said antenna system and said loop winding when said primary coil and said loop winding are intimately juxtaposed.

9. An antenna circuit for a radio receiver, constructed and arranged to provide reception selectively from a loop or from an external antenna, comprising a loop winding, a coupling winding, and a tuning condenser connected to form a resonant loop tuning circuit capable of being tuned over a predetermined range of frequencies, said coupling winding having an inductance which is small compared to the inductance of said loop winding, an external antenna and a high impedance primary winding in circuit therewith, said last-named winding being tightly coupled to said coupling winding.

10. An antenna circuit according to claim 9, characterized in that means are provided for short-circuiting said high impedance primary winding to provide pure loop reception substantially unaffected by said antenna or said high impedance primary.

11. An antenna system for a modulated-carrier signal receiver adapted to operate from a loop antenna or from an antenna-ground system comprising, a loop antenna adapted to be tuned over a frequency band, means for coupling said loop antenna to said receiver, an input circuit adapted to be connected to an antenna-ground system having capacitance, impedance means coupled to said loop and tunable by said antenna capacitance to resonance at a frequency near the lower end of said band, and means for selectively con necting said last-named means to said input circuit to couple said antenna-ground system through said loop antenna to said receiver.

12. An antenna system for a modulated-carrier signal receiver adapted to operate from a loop antenna or from an antenna-ground system comprising, a loop antenna adapted to be tuned over a frequency band, means for coupling said loop antenna to said receiver, an input circuit adapted to be connected to an antenna-ground system having capacitance, a primary circuit including a concentrated winding of cross-sectional area, perpendicular to its axis, small in comparison to that of said loop, said winding being positioned in inductive relation to said loop and being tunable by said antenna capacitance to resonance at a frequency near the lower end of said band, and means for selectively connecting said primary circuit to said input circuit to couple said antenna-ground system through said loop antenna to said receiver.

13. An antenna system for a modulated-carrier signal receiver adapted to operate from a loop antenna or from an antenna-ground system comprising, a loop antenna adapted to be tuned over a frequency band, means for coupling said loop antenna to said receiver, an input circuit adapted to be connected to an antenna-ground system having capacitance, a primary circuit including an inductor coupled to said loop, said primary circuit being tunable by said antenna capacitance to resonance at a frequency near the lower end of said band, and means for selectively connecting said primary circuit to said input circuit to couple said antenna-ground system through said loop antenna to said receiver.

14. An antenna circuit for a radio receiver, constructed and arranged to provide reception selectively from a loop or from an external antenna, comprising a loop winding and a tuning condenser connected in a closed resonant circuit capable of being tuned over a predetermined range of frequencies, an external antenna system, a primary circuit coil having a high inductance connected serially in said external antenna system, said coil together with said antenna system forming a circuit which is selfresonant near the low frequency end of said tuning range, and means including a winding whose inductance is small compared with the inductance of said primary circuit coil for inductively coupling said external antenna system to said closed resonant circuit.

15. In combination with a radio receiver, a resonant loop circuit comprising a loop winding and a tuning condenser, an external antenna, and means including a high impedance primary winding for inductively coupling said antenna to said resonant loop circuit.

16. In combination with a radio receiver, a resonant loop circuit comprising a loop winding and a tuning condenser, an external antenna, and means including a high impedance primary winding for inductively coupling said antenna to said resonant loop circuit, the resonant frequency of said high impedance primary winding with said external antenna attached being lower than the lowest frequency to which said winding can be tuned by said tuning condenser.

WILLIAM H. NEWBOLD. 

